As hydrocarbon reservoirs become more difficult to reach, wellbore drilling operations become more complex both vertically and horizontally, and the need to precisely locate a drilling assembly within desired subterranean formations increases. This requires accurately steering the drilling assembly either to avoid particular formations or to intersect formations of interest. Steering the drilling assembly includes changing the tool face direction of a drill bit coupled to the end of the drilling assembly.
Rotary steerable tools are commonly used in directional drilling operations and can include an offset mandrel or other assembly that may be coupled to a rotating housing. It may be desirable to control the rotation of the offset mandrel independently from the rotation of the housing and otherwise maintain the offset mandrel in a geostationary position with respect to the formations being penetrated by the drill bit. In some rotary steerable systems, the drill bit may be operatively coupled to the offset mandrel via a bit shaft. It may be desirable to control the rotation of the offset mandrel and, therefore, the orientation of the bit shaft and drill bit, independently of the rotation of the drill string and the drill bit. Responsive control of the rotation of the offset mandrel may reduce overall rig time by ensuring that the wellbore is drilled according to a desired well plan.